Oxygen and nutrients are needed to maintain normal metabolic function of all living tissue. This is especially true for retinal cells. Abnormalities in retinal oxygen delivery and consumption are thought to significantly contribute to the development of retinal diseases. In addition to the role played in acute retinal artery embolic disease, retinal vein occlusion, retinopathy of prematurity and diabetic retinopathy, derangements in retinal oxygenation may also be involved in the development of glaucoma and age-related macular degeneration.
Several techniques have been developed for studying retinal oxygenation based on assessment of choroidal and retinal circulations. Multiwavelength reflectance spectrophotometry measures oxygen saturation of blood in the retinal vasculatures, but the relationship between oxygen tension (pO2) and oxygen saturation of hemoglobin is variable depending on metabolic conditions. Laser Doppler methods have been utilized for measurement of blood flow in retinal and choroidal vasculatures but such methods only provide an indirect measure of vascular pO2.
Retinal tissue oxygenation has also been studied by imaging methods and oxygen-sensitive microelectrodes. Magnetic resonance imaging has been used to study retinal oxygenation response, an indirect measure of retinal tissue pO2, with limited resolution as compared with optical techniques. A fluorescence imaging technique for measurement of retinal pO2 has been reported, but with limited depth resolution. Oxygen-sensitive microelectrodes, measure retinal pO2 directly and with a high depth resolution, but the clinical utility of this technique is limited due to its invasive nature of physically penetrating the tissue. Additionally, microelectrode measurements are typically limited to one-dimensional linear profiles.
There exists a need for improved methods and apparatus for measurement of tissue pO2, especially in the retinal vasculature and tissue. New technologies for assessment of retinal oxygenation are needed to broaden knowledge on disease pathophysiology, and advance diagnostic and therapeutic procedures. In particular, techniques for accurate and precise measurements of oxygen tension would satisfy a long felt need in the field for better diagnostic tools for assessment of retinal function and/or detection of retinal pathologies associated with hypoxia.